Traditional metal element analysis methods include atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry/mass spectrometry, etc. The detecting instruments used in these methods are expensive and bulky, the detection procedures are cumbersome, and the detection costs are high. With the development of science and technology and improvement in detection level, people began to study simple, rapid, and low-cost detection technology for metal elements.
Microplasma is a general term for plasmas with dimensions on the order of millimeters or less. The micro-discharge plasma can usually operate under atmospheric pressure, usually without any special gas, and thus its operating cost is low and the instrument therefor is small in size. The solution cathode glow discharge device is such a device that, at atmospheric pressure, the sample solution acts as a cathode and the metal rod acts as an anode. By applying a high voltage between the electrodes, gas discharge is generated between the electrodes. During the discharge process, the solution of the solution electrode is continuously vaporized, so that the metal ions dissolved in the solution also enter into the plasma and are excited to generate spectral radiation, and thus the detection of metal ions in the solution can be realized, in combination with a spectrometer. It not only has the advantages such as low cost as atomic absorption spectrometry, high flux, multi-element, and high sensitivity as emission spectrometry, but also has the advantages such as having a simple structure, small size, low power consumption, the ability to operate under atmospheric pressure, no requirement for a nebulizer or vacuum system, and ease of miniaturization and on-line analysis. Therefore, it is widely used in the field of atomic spectrometry.
The sample is introduced into the solution cathode glow discharge device in the form of a liquid. That is, the liquid sample is introduced into the glass capillary via the sample introduction tube by the peristaltic pump and overflows. The sample introduction method is simple and only liquid samples can be tested; moreover, since the pH of the cathode liquid must be 1, the requirements for pretreatment of the sample are strict, which severely restricts its application in the analysis field. At the same time, the nebulization efficiency of the elements in the solution to be measured is low in the plasma evaporation, and the sensitivity of element to be measured is reduced. Therefore, to improve its sample introduction method, especially to achieve gas sample introduction, can not only simplify the sample pre-treatment process and broaden the application of micro-plasma, but also improve its test sensitivity, and provide the possibility for use in combination with other instruments.
Conventional spectroscopic-based metal ion detection methods mainly include atomic absorption spectrometry and atomic emission spectrometry. The detecting instruments commonly used in these methods include flame atomic absorption spectrometry, inductively coupled plasma emission spectrometry, and the like. However, these commonly used detecting instruments are bulky, expensive, and have high detection costs and are difficult to use for field analysis and monitoring. With the development of technology and improvement in detection levels, people began to study simple, rapid, and low-cost metal element detection technology, in order to achieve rapid and effective monitoring of metal residues in the environment to protect public health and ecological security.
Solution cathode glow discharge spectrometry detection technology has the advantages of simple structure, small size, low operating power consumption, ability to operate under normal pressure, no nebulizer, no vacuum system, easy realization of miniaturization and on-line analysis, etc., and is promising for application in metal ion detection in various fields such as geology, environmental protection, materials science, food safety, water purification, etc.
Although solution cathode glow discharge spectrometry has relatively low detection limits for most elements, such as Li, Na, etc., it has low sensitivity to most heavy metal elements, especially toxic heavy metal elements, such as Se, Te, Hg, As, Sb, Bi, Pb, etc. At present, scientists have improved the sensitivity of certain elements by adding small-molecule organic acids or surfactants and achieved good results. However, there are still problems as follows: on one hand, the improvement of sensitivity is limited, it only has a good effect on some elements, while it is still not universally suitable for many toxic heavy metal elements, and it cannot fully meet the needs of environmental monitoring; on other hand, although elemental morphology analysis can be performed by methods such as liquid chromatography separation or solid-phase separation of new materials, the process is relatively complicated and the cost is relatively high.
The use of chemical reactions to form volatile gases from the analyte is not only an effective way to increase the sensitivity and selectivity of the analytical method, but also a special technique. Among them, the most advanced is the hydride generation technology, which is combined with conventional instrument detection methods such as inductively coupled plasma emission spectrometry and graphite furnace atomic absorption spectrometry, to achieve gas sample introduction.
Compared with the conventional sample introduction method, the hydride generation sample introduction technique enables the component to be measured to be separated from the matrix in the form of gas, reducing the matrix interference, and enriching the element to be measured, so that the sample introduction efficiency increases to nearly 100% from <5% in the case of pneumatic nebulization; at the same time, the easy dissociation of gas hydride greatly improved the atomization efficiency, and thus the detection limit and precision during measurement can be greatly improved, and the morphological analysis and simultaneous detection of multiple elements can be realized.